Carburetor



g- 1961 Q E. L. RAPPLEAN 2,995,350

CARBURETOR Filed 001. 11, 1957 2 Sheets-Sheet 1 F IG.7.

INVENTOR. EUGENE L. RAPFLEAN ATTORNEY Aug. S, 1961 E. I... RAPPLEAN CARBURETOR 2 Sheets-Sheet 2 Filed Oct. 11, 1957 2/ INVENTOR.

EUGENE L. RAPPLEAN ATTORNEY United States Patent C) 2,995,350 CARBURETOR Eugene L. Rapplean, Ferguson, Mo., assignor to ACF Industries, Incorporated, New York, 'N.Y., a corporation of New Jersey Filed Oct. 11, 1957, Ser. No. 689,688 4 Claims. (Cl. 261-41) This invention relates to fuel systems for internal combustion engines and more particularly to an improved carburetor.

In carburetors, generally, a ditferential in pressure draws fuel from a fuel chamber into a mixture conduit in the carburetor, and then into the engine. In order to properly calibrate a carburetor to provide the required fuel under varying engine operation conditions, the fuel pressure in the carburetor fuel chamber should be regulated. During idling of the engine, a butterfly throttle valve in the carburetor mixture conduit is closed, and fuel is drawn into the mixture conduit from the fuel chamber through an idle port in the mixture conduit either at or downstream from the throttle. During normal or high speed operation of the engine, fuel is drawn from the fuel chamber through a main orifice upstream from the open throttle valve, and into the mixing chamber. When the throttle is closed as during idling, the main orifice is subjected to a substantially higher pressure than is the idling port. Similarly, during normal or high speed operation, air at the main orifice passes through a venturi, and the pressure is substantially lower than at the idle port. Either set of conditions may result in back bleeding, that is, drawing air through the orifice or port exposed to the higher pressure and into the fuel supply, thereby disrupting the regulation of the fuel pressure. To overcome this condition, it is common practice to utilize a check valve in the fuel system through which back bleeding occurs. Although a check valve normally performs satisfactorily, it increases the cost of the carburetor, and is subject to sticking and other malfunction. Under certain conditions, the check valve can merely be eliminated, but this has not proved to be entirely satisfactory.

It is, therefore, an object of this invention to prevent back bleeding into a controlled pressure fuel supply of a carburetor.

Another object of this invention is to prevent such back bleeding without relying on check valves in either the main or idle fuel systems of the carburetor.

Another object of this invention is to provide an improved carburetor which is relatively simple and inexpensive to manufacture and more reliable to use.

Additional objects and advantages will be apparent from the following description and the accompanying drawings, wherein:

FIG. 1 is a top plan view showing a combined carburetor and pump unit illustrating an embodiment of the invention, the unit being shown as applied to a twocycle engine crankcase.

FIG. 2 is a side elevation view of the carburetor shown in FIG. 1.

FIG. 3 is an enlarged transverse sectional view taken in the plane indicated by the line 3-3 in FIG. 1, with parts removed.

FIG. 4 is an enlarged fragmentary sectional view illustrating the main or high speed fuel system.

FIG. 5 is an enlarged fragmentary vertical sectional view illustrating the idle fuel system.

FIG. 6 is a diagrammatic view of the combination carburetor and pump unit during idling operation, and

FIG. 7 is a schematic view showing the combined carburetor and pump unit as applied to a four-cycle engine.

Patented Aug. 8, 1961 Briefly, the invention relates to a carburetor having both an idle fuel system and a main or high speed fuel system supplied from a common source of supply, such as a fuel chamber, in which the pressure of the fuel is regulated, as by a pressure sensing diaphragm. Other means of regulating the pressure of the fuel, such as a float system, are applicable. A by-pass is provided between the idle fuel system and the main fuel system to prevent back bleeding of air through the fuel systems and into the fuel chamber, thereby disrupting the pressure regulation.

Referring to the drawings, and more particularly to FIGS. 1 to 3, the combined carburetor and fuel pump unit is shown as comprising a body 1 formed with a mixture conduit 2 having an inlet 3, a venturi 4, and an outlet 5. A flange 6 is provided on the body 1 for bolted engagement on a crankcase 7 of a conventional two-cycle internal combustion engine to supply a fuel mixture from the mixture conduit into the crankcase during operation of the engine.

A choke valve 8 is provided in the inlet 3 and secured to a shaft 9 journaled at its ends in the body 1. A choke control lever 10 is secured on one end of the shaft 9 for rotating the choke valve 8 in any conventional manner between its open and closed positions.

A throttle valve 11 is provided in the mixture conduit outlet 5, and is secured to a shaft 12 journaled at its ends in the body 1. A throttle control lever 13 is secured to one end of the shaft 12 and formed with an arm 14 for abutting engagement against an idle adjustment screw 15 on the body 1 when the throttle valve is disposed in its closed or idle position. A helical torsion spring 15a is mounted on the shaft 12 to yieldably resist movement of the arm 14 away from the idle adjustment screw 15, one end of the spring being secured to the body 1 and the other end thereof engaging the throttle control lever 13.

A flexible, resilient, pressure sensing diaphragm 16 has its marginal portion clamped between a base plate 17 and a lower flange 18 on the body 1 by means of cap screws 19. As illustrated in FIG. 3, the diaphragm 16 serves as a movable partition between a fuel chamber 20 in the body and an atmospheric chamber 21 in the base plate 17 vented as to the atmosphere through an air vent 22. The diaphragm 16 is preferably of the type shown and described in Patents 2,595,127 and 2,734,009, comprising a textile fabric coated on both sides with cured synthetic rubber.

A flexible, resilient pump diaphragm 23 has its marginal portion clamped between a cover 24 and an upper flange 25 on the body by cap screws 26, and is preferably formed of diaphragm material of the type disclosed in the above mentioned patents. The diaphragm 23 provides a movable partition between a pump chamber 27 in the body 1 and an impulse chamber 28 in the cover 24.

As illustrated in FIG. 3, the diaphragm 23 is provided with a U-shaped slot 29 to form a conventional flat inlet check valve 30 cooperating with a valve port 31 leading from a main fuel inlet 32 into a fuel transfer chamber 33 having a compression spring 34 therein to yieldably resist movement of the check valve 30 from its seat 35. A common fuel inlet-outlet passage 36 is provided in the body 1 between the transfer chamber 33 and the pump chamber 27, and a main fuel inlet passage 37 leads from the check valve 30 to the fuel chamber 20. It should be noted that the transfer chamber 33 forms part of the main fuel inlet passage 37 and communicates with the pump chamber 27 by means of the single inlet-outlet fuel passage 36, whereby movements of the pum diaphragm 23 cause fuel to flow back and forth in the passage 36.

A needle valve body 38 is threaded into the outlet end of the main fuel inlet passage 37 and is formed with a restricted port 39 and an annular valve seat 40. A needle valve 41 is slidably mounted in the valve body 38 and is formed with a tapered end 42 to engage the valve seat 40. The other end 43 of the needle valve is rounded for engagement thereof by one end of an inlet control lever 44. The needle valve 41 is adapted to be inexpensively manufactured from nylon rod stock, and provided with a rather blunt, tapered end 42 having a taper of, for example, to prevent sticking of the tapered end in the valve seat 40.

The control lever 44 is pivotally mounted intermediate its ends upon a pivot pin 45 secured to the body 1, and is provided with a spring seat 46 to receive one end of a compression spring 47 having its other end seated against the body 1. Disks 48 and 49 are secured to opposite sides of the pressure sensing diaphragm 16 by means of a rivet 50 which is adapted to engage the spring seat end 46 of the control lever 44 to open the needle valve 41.

As illustrated in FIG. 4, a main fuel outlet passage 51 leads from the fuel chamber 20 to a fuel discharge passage 52 having an orifice 53 opening into the throat of the venturi 4. A valve seat 54 is formed in the body 1 at the entrance to the discharge passage 52 to receive the tapered end 55 of a main or high speed adjustment screw 56 threaded into the body 1.

As best seen in FIG. 5, the body 1 is also provided with an idle fuel circuit including an outlet passage 57 from the fuel chamber 20 to a short passage 58 opening into a passage 59 which, in turn, opens into a punch chamber 60 and then into an idle port 61. The punch chamber 60 is sealed by a Welch plug 62. A restricted orifice 63 is provided at the inlet end of the passage 57, and an idle adjustment orifice 64 is provided in the inlet of the short passage 58 to receive the tapered end 65 of an idle adjustment screw 66 threaded into the body 1. The idle port 61 leads into the outlet 5 of the mixture conduit 2, and is located adjacent or partially posterior to the throttle valve 11 when the latter is disposed in its idle position.

A by-pass passage 67 interconnects the outlet passage 51 of the main fuel system and the punch chamber 60 of the idle system. The passage 67 prevents air from entering the fuel chamber 20 and disturbing the fuel pressure regulation therein, through either the main orifice 53 or the idle port 61 when the other is functit ning. As is most clearly illustrated in FIG. 6, the by-pass passage joins the main fuel system between the valve 55 and the fuel chamber 20, and the idle fuel s stem between the valve 65 and the idle port 61. A cali' 'ated restriction 68 is provided in the by-pass 67.

Referring to FIGS. 1 and 3, an air passage 69 leads through the cover 24 into body 1 from the impulse chamber 28 to an opening 70 in the crankcase 7 of the engine. A nipple 71 is mounted in the main fuel inlet 32 to receive one end of a fuel line 72 leading to a fuel tank 73.

In the operation of the combined carburetor and fuel pump thus described, pressure pulsations within the crankcase 7 of a two-cycle internal combustion engine are transmitted through the passage 69 and impulse chamber 28 to the pump diaphragm 23 to cause a flow of fuel from the fuel inlet 32 past the check valve 35 into and through the fuel passage 37 and thence past the needle valve 41 into the fuel chamber 20.

During high speed operation of the engine, fuel is delivered from the fuel chamber 20 through the main fuel passage 51 and orifice 53 into the throat of the venturi 4 during each induction stroke of the engine, at which time the differential in pressure on opposite sides of the diaphragm 16 causes the latter to engage and pivot the control lever 44 in a direction to permit the needle valve 41 to open. After each induction stroke, the spring 47 acts through the lever 44 to close the needle valve 41.

It should be noted that the flow of fuel from the inlet 32 to the fuel chamber 20 is controlled by the inlet check valve 35 and needle valve 41. As the pump diaphragm 23 and pressure sensing diaphragm 16 are both actuated during each induction stroke of the engine, it would appear to be necessary to provide an outlet check valve for the pump to be located in the passage 37. As the unit shown and described has proved to be operative in supplying sufiicient fuel to an engine to satisfy its requirements, it appears that the pump must draw in fuel from the fuel inlet 32 prior to opening of the needle valve 41 by the diaphragm 16. Such an operation may be due to an excessive quantity of fuel in the fuel chamber 20, which delays engagement of the rivet 50 on diaphragm 16 against the lever 44 until the pump diaphragm 23 has acted to draw fuel into the passage 37. The unit shown and described is adapted to operate more efiiciently without a reverse flow check valve in the fuel outlet passage 51 because of by-pass 67.

The by-pass 67 functions as follows: When the engine is operating at normal or high speeds, air is drawn through the mixture conduit 2 and a reduction occurs at the venturi 4, thereby drawing fuel out through the main orifice 53. During such operation, the throttle 11 is open and the fuel-air mixture passing idle port 61 is at a substantially higher pressure than at the main orifice 53. Therefore, the air-fuel mixture may be drawn through the idle port 61 and into the idle system. However, when this occurs, the mixture is drawn through by-pass 67 rather than into the fuel chamber 20, and out through the main orifice 53. Thus, the pressure regulation in the fuel chamber 20 is not disrupted. When the engine is at idle, the throttle valve 11 is closed, as illustrated in FIG. 6. The reduced pressure in the outlet 5 of the mixture conduit 2 draws fuel from the fuel chamber 20 out of the idle port '61. As the flow of air through the venturi 4 is very slight, insufiicient reduction in pressure exists at the main orifice 53 to draw fuel from the fuel chamber 20 through the main orifice 53. Instead, because fuel is being drawn out of the idle port 61, air in the inlet end 3 of the mixture conduit 2 may be drawn through the orifice 53, but rather than passing into the fuel chamber 20, the air passes through by-pass 67 and out idle port 61. The reduced pressure acting on the fuel in the main system passage 51 tends to draw fuel in the direction of main orifice 53, rather than toward the fuel chamber 20, as would occur, in the absence of by-pass 67, and, therefore, reduces the transition time from idle to main fuel system operation. Similar forces draw fuel through the idle system and toward the idle port 61 during normal or high speed operation.

To eliminate a check valve between the fuel chamber 20 and the main orifice 53 and still positively prevent back bleeding into the fuel chamber, the by-pass passage 67 is provided between the main fuel passageway system and the idle fuel passageway system. The by-pass resistance and the combined variable and fixed resistances must be so calibrated that the path of least resistance from the idle port 61 to the main orifice 53 is through the by-pass 67 rather than through the fuel chamber 20. Such calibration is well understood by those skilled in the art to which this invention pertains.

FIG. 7 illustrates schematically a modified form of the invention in which the combined carburetor and pump 75 is shown as applied to a one-cylinder four-cycle internal combustion engine 76 having an intake manifold 77 and a crankcase 78. In this form of the invention, the flange 6 is bolted to the manifold 77, and a conduit 79 leads from the crankcase 78 to the impulse chamber 28 of the pump, whereby pressure pulsations in the crankcase are transmitted to the pump diaphragm 23. This form of the invention is otherwise similar to the form heretofore shown and described.

It should be noted that the invention is equally applicable to many other types of carburetors in which a regulated pressure should be maintained in a fuel supply.

A float system provides another example of a carburetor in which the invention may be utilized.

Although this invention has been described with particular reference to certain features, embodiments, and a particular structure which fulfills the objects of the present invention, various modifications therein will be apparent to one skilled in the art, and the invention is, therefore, not to be limited to such features, embodiments, and specific stnlcture previously described, except to the extent set forth in the appended claims.

I claim:

1. In a charge forming device for an internal combustion engine, a body having a horizontal mixture conduit therein, a venturi in said conduit, a butterfly throttle valve in said mixture conduit posterior to said venturi, a fuel reservoir in said body below said conduit, a main fuel discharge orifice to discharge into said venturi when said valve is open, an idle fuel discharge orifice to discharge into said conduit adjacent said throttle valve when the latter is closed, a short first passage connecting said reservoir with said main fuel discharge orifice, a short second passage connecting said reservoir with said idle fuel discharge orifice, and a by-pass interconnecting said first and second passages intermediate their ends, whereby air and fuel from either the first or second passage is drawn through said by-pass into the other passage and thence into the mixture conduit responsive to operation of said throttle valve between its open and closed positions.

2. In a charge forming device for an internal combustion engine, a body having a horizontal mixture conduit therein, a venturi in said conduit, a butterfly throttle valve in said mixture conduit posterior to said venturi, a fuel reservoir in said body below said conduit, :1 main fuel discharge orifice to discharge into said venturi when said valve is open, an idle fuel discharge orifice to discharge into said conduit adjacent said throttle valve when the latter is closed, a short first passage connecting said reservoir with said main fuel discharge orifice, a short second passage connecting said reservoir with said idle fuel discharge orifice, and a by-pass interconnecting said first and second passages intermediate their ends, whereby air and fuel from either the first or second passage is drawn through said by-pass into the other passage and thence into the mixture conduit responsive to operation of said throttle valve between its open and closed positions, a first metering restriction in said first passage, 2. second metering restriction in said second passage, the juncture of said by-pass and first passage being between said first metering restriction and said reservoir, and the juncture of said by-pass and second passage being between said second metering restriction and said idle fuel discharge orifice.

3. In a charge forming device for an internal combustion engine, a body having a horizontal mixture conduit therein, a venturi in said conduit, a butterfly throttle valve in said mixture conduit posterior to said venturi, a fuel reservoir in said body below said conduit, a main fuel discharge orifice to discharge into said venturi when said valve is open, an idle fuel discharge orifice to discharge into said conduit adjacent said throttle valve when the latter is closed, a short first passage connecting said reservoir with said main fuel discharge orifice, a short second passage connecting said reservoir with said idle fuel discharge orifice, and a by-pass interconnecting said first and second passages intermediate their ends, whereby air and fuel from either the first or second passage is drawn through said by-pass into the other passage and thence into the mixture conduit responsive to operation of said throttle valve between its open and closed positions, a first metering restriction in said first passage, a second metering restriction in said second passage, the juncture of said by-pass and first passage being between said first metering restriction and said reservoir, and the juncture of said by-pass and second passage being between said second metering restriction and said idle fuel discharge orifice, and individual means for varying the size of said restrictions.

4. In a charge forming device for an internal combustion engine, a body having a horizontal mixture conduit therein, a venturi in said conduit, a butterfly throttle valve in said mixture conduit posterior to said venturi, a fuel reservoir in said body below said conduit, a main fuel discharge orifice to discharge into said venturi when said valve is open, an idle fuel discharge orifice to discharge into said conduit adjacent said throttle valve when the latter is closed, a short first passage connecting said reservoir with said main fuel discharge orifice, a short second passage connecting said reservoir with said idle fuel discharge orifice, and a by-pass interconnecting said first and second passages intermediate their ends, whereby air and fuel from either the first or second passage is drawn through said by-pass into the other passage and thence into the mixture conduit responsive to operation of said throttle valve between its open and closed positions, a first metering restriction in said first passage, a second metering restriction in said second passage, the juncture of said by-pass and first passage being between said first metering restriction and said reservoir, and the juncture of said by-pass and second passage being between said second metering restriction and said idle fuel discharge orifice, and individual means for varying the size of said restrictions, and a metering restriction in said by-pass.

References Cited in the file of this patent UNITED STATES PATENTS 2,568,987 Brunner Sept. 25, 1951 2,676,004 Bimberg Apr. 20, 1954 2,713,854 Conover July 26, 1955 2,796,838 Phillips June 25, 1957 2,801,621 Andersonet a1. Aug. 6, 1957 2,841,372 Phillips July 1, 1958 2,875,990 Gretz Mar. 3, 1959 

